Chapter 12

Chapter 12

Be Prepared

12.1

5, 7, 9, 11

12.2

−1 , 1 , −1 , 1 −1 , 1 , −1 , 1

12.3

20

12.4

3, 7, 11, 15

12.5

( 5 , 2 ) ( 5 , 2 )

12.6

654

12.7

3 4 3 4

12.8

ⓐ 81; ⓑ 116116

12.9

ⓐ 12; ⓑ 36; ⓒ 108

12.10

35

12.11

9 x 2 + 30 x + 25 9 x 2 + 30 x + 25

12.12

x 2 − 2 x y + y 2 x 2 − 2 x y + y 2

Try It

12.1

−1 , 2 , 5 , 8 , 11 −1 , 2 , 5 , 8 , 11

12.2

−3 , −1 , 1 , 3 , 5 −3 , −1 , 1 , 3 , 5

12.3

7 , 13 , 31 , 85 , 247 7 , 13 , 31 , 85 , 247

12.4

−3 , −1 , 3 , 11 , 27 −3 , −1 , 3 , 11 , 27

12.5

−1 , 4 , −9 , 16 , −25 −1 , 4 , −9 , 16 , −25

12.6

1 , −8 , 27 , −64 , 125 1 , −8 , 27 , −64 , 125

12.7

a n = 3 n a n = 3 n

12.8

a n = 5 n a n = 5 n

12.9

a n = ( −1 ) n 3 n a n = ( −1 ) n 3 n

12.10

a n = ( −1 ) n + 1 n 2 a n = ( −1 ) n + 1 n 2

12.11

a n = 1 2 n a n = 1 2 n

12.12

a n = 1 n 2 a n = 1 n 2

12.13

2 , 1 , 1 3 , 1 12 , 1 60 2 , 1 , 1 3 , 1 12 , 1 60

12.14

3 , 3 2 , 1 2 , 1 8 , 1 40 3 , 3 2 , 1 2 , 1 8 , 1 40

12.15

1 2 , 1 6 , 1 12 , 1 20 , 1 30 1 2 , 1 6 , 1 12 , 1 20 , 1 30

12.16

1 2 , 1 3 , 1 4 , 1 5 , 1 6 1 2 , 1 3 , 1 4 , 1 5 , 1 6

12.17

45

12.18

60

12.19

16 3 16 3

12.21

∑ n = 1 5 1 2 n ∑ n = 1 5 1 2 n

12.22

∑ n = 1 5 1 n 2 ∑ n = 1 5 1 n 2

12.23

∑ n = 1 5 ( −1 ) n + 1 n 2 ∑ n = 1 5 ( −1 ) n + 1 n 2

12.24

∑ n = 1 5 ( −1 ) n 2 n ∑ n = 1 5 ( −1 ) n 2 n

12.25

ⓐ The sequence is arithmetic with common difference d=11d=11. ⓑ The sequence is arithmetic with common difference d=−6d=−6.
ⓒ The sequence is not arithmetic as all the differences between the consecutive terms are not the same.

12.26

ⓐ The sequence is not arithmetic as all the differences between the consecutive terms are not the same. ⓑ The sequence is arithmetic with common difference d=2.d=2.
ⓒ The sequence is arithmetic with common difference d=−5.d=−5.

12.27

7 , 3 , −1 , −5 , −9 , … 7 , 3 , −1 , −5 , −9 , …

12.28

11 , 3 , −5 , −13 , −21 , … 11 , 3 , −5 , −13 , −21 , …

12.29

241

12.30

−106 −106

12.31

a11=2.a11=2. The general term is an=−3n+35.an=−3n+35.

12.32

a19=−55.a19=−55. The general term is an=−4n+21.an=−4n+21.

12.33

a1=5,a1=5,d=4.d=4. The general term is an=4n+1.an=4n+1.

12.34

a1=8,a1=8,d=−3.d=−3. The general term is an=−3n+11.an=−3n+11.

12.35

1,890

12.36

1,515

12.37

2,300

12.38

5,250

12.39

2,670

12.40

3,045

12.41

ⓐ The sequence is geometric with common ratio r=3.r=3. ⓑ The sequence is geometric with common ratio r=14.r=14. ⓒ The sequence is not geometric. There is no common ratio.

12.42

ⓐ The sequence is not geometric. There is no common ratio. ⓑ The sequence is geometric with common ratio r=2.r=2. ⓒ The sequence is geometric with common ratio r=12.r=12.

12.43

7 , −21 , 63 , −189 , 567 7 , −21 , 63 , −189 , 567

12.44

6 , −24 , 96 , −384 , 1536 6 , −24 , 96 , −384 , 1536

12.45

1 6,561 1 6,561

12.46

1 16,384 1 16,384

12.47

a9=39,366.a9=39,366. The general term is an=6(3)n−1.an=6(3)n−1.

12.48

a11=7,168.a11=7,168. The general term is an=7(2)n−1.an=7(2)n−1.

12.49

3,145,725 3,145,725

12.50

10,460,353,200 10,460,353,200

12.51

393,204 393,204

12.52

10,230 10,230

12.53

96

12.54

256 3 256 3

12.55

4 9 4 9

12.56

8 9 8 9

12.57

$ 10,000 $ 10,000

12.58

$ 3 , 333.33 $ 3 , 333.33

12.59

$ 88,868.36 $ 88,868.36

12.60

$ 698,201.57 $ 698,201.57

12.61

x 5 + 5 x 4 y + 10 x 3 y 2 + 10 x 2 y 3 x 5 + 5 x 4 y + 10 x 3 y 2 + 10 x 2 y 3
+ 5 x y 4 + y 5 + 5 x y 4 + y 5

12.62

p 7 + 7 p 6 q + 21 p 5 q 2 + 35 p 4 q 3 p 7 + 7 p 6 q + 21 p 5 q 2 + 35 p 4 q 3
+ 35 p 3 q 4 + 21 p 2 q 5 + 7 p q 6 + q 7 + 35 p 3 q 4 + 21 p 2 q 5 + 7 p q 6 + q 7

12.63

x 4 + 8 x 3 + 24 x 2 + 32 x + 16 x 4 + 8 x 3 + 24 x 2 + 32 x + 16

12.64

x 6 + 6 x 5 + 15 x 4 + 20 x 3 + 15 x 2 x 6 + 6 x 5 + 15 x 4 + 20 x 3 + 15 x 2
+ 6 x + 1 + 6 x + 1

12.65

16 x 4 − 96 x 3 + 216 x 2 − 216 x + 81 16 x 4 − 96 x 3 + 216 x 2 − 216 x + 81

12.66

64 x 6 − 192 x 5 + 240 x 4 − 160 x 3 64 x 6 − 192 x 5 + 240 x 4 − 160 x 3
+ 60 x 2 − 12 x + 1 + 60 x 2 − 12 x + 1

12.67

ⓐ 6 ⓑ 1 ⓒ 1 ⓓ 35

12.68

ⓐ 2 ⓑ 1 ⓒ 1 ⓓ 6

12.69

x 5 + 5 x 4 y + 10 x 3 y 2 + 10 x 2 y 3 x 5 + 5 x 4 y + 10 x 3 y 2 + 10 x 2 y 3
+ 5 x y 4 + y 5 + 5 x y 4 + y 5

12.70

m 6 + 6 m 5 n + 15 m 4 n 2 + 20 m 3 n 3 m 6 + 6 m 5 n + 15 m 4 n 2 + 20 m 3 n 3
+ 15 m 2 n 4 + 6 m n 5 + n 6 + 15 m 2 n 4 + 6 m n 5 + n 6

12.71

x 5 − 15 x 4 + 90 x 3 − 270 x 2 x 5 − 15 x 4 + 90 x 3 − 270 x 2
+ 405 x − 243 + 405 x − 243

12.72

y 6 − 6 y 5 + 15 y 4 − 20 y 3 + 15 y 2 y 6 − 6 y 5 + 15 y 4 − 20 y 3 + 15 y 2
− 6 y + 1 − 6 y + 1

12.73

243 x 5 − 810 x 4 y + 1080 x 3 y 2 243 x 5 − 810 x 4 y + 1080 x 3 y 2
− 720 x 2 y 3 + 240 x y 4 − 32 y 5 − 720 x 2 y 3 + 240 x y 4 − 32 y 5

12.74

256 x 4 − 768 x 3 y + 864 x 2 y 2 256 x 4 − 768 x 3 y + 864 x 2 y 2
− 432 x y 3 + 81 y 4 − 432 x y 3 + 81 y 4

12.75

15 x 4 y 2 15 x 4 y 2

12.76

70 a 4 b 4 70 a 4 b 4

12.77

3,584

12.78

280

Section 12.1 Exercises

1.

−5 , −3 , −1 , 1 , 3 −5 , −3 , −1 , 1 , 3

3.

4 , 7 , 10 , 13 , 16 4 , 7 , 10 , 13 , 16

5.

5 , 7 , 11 , 19 , 35 5 , 7 , 11 , 19 , 35

7.

1 , 5 , 21 , 73 , 233 1 , 5 , 21 , 73 , 233

9.

2 , 1 , 8 9 , 1 , 32 25 2 , 1 , 8 9 , 1 , 32 25

11.

1 , 3 2 , 5 4 , 7 8 , 9 16 1 , 3 2 , 5 4 , 7 8 , 9 16

13.

−2 , 4 , −6 , 8 , −10 −2 , 4 , −6 , 8 , −10

15.

1 , −4 , 9 , −16 , 25 1 , −4 , 9 , −16 , 25

17.

1 , − 1 4 , 1 9 , − 1 16 , 1 25 1 , − 1 4 , 1 9 , − 1 16 , 1 25

19.

a n = 8 n a n = 8 n

21.

a n = n + 5 a n = n + 5

23.

a n = e n + 2 a n = e n + 2

25.

a n = ( −1 ) n 5 n a n = ( −1 ) n 5 n

27.

a n = ( −1 ) n n 3 a n = ( −1 ) n n 3

29.

a n = ( −1 ) n 2 n a n = ( −1 ) n 2 n

31.

a n = 1 4 n a n = 1 4 n

33.

a n = − n n + 1 a n = − n n + 1

35.

a n = − 5 2 n a n = − 5 2 n

37.

4 , 2 , 2 3 , 1 6 , 1 30 4 , 2 , 2 3 , 1 6 , 1 30

39.

3 , 6 , 18 , 72 , 360 3 , 6 , 18 , 72 , 360

41.

2 , 24 , 720 , 40320 , 3628800 2 , 24 , 720 , 40320 , 3628800

43.

1 , 1 2 , 1 3 , 1 4 , 1 5 1 , 1 2 , 1 3 , 1 4 , 1 5

45.

1 , 1 2 , 2 3 , 3 2 , 24 5 1 , 1 2 , 2 3 , 3 2 , 24 5

47.

2 , 3 2 , 8 3 , 15 2 , 144 5 2 , 3 2 , 8 3 , 15 2 , 144 5

49.

1 + 4 + 9 + 16 + 25 = 55 1 + 4 + 9 + 16 + 25 = 55

51.

5 + 7 + 9 + 11 + 13 + 15 = 60 5 + 7 + 9 + 11 + 13 + 15 = 60

53.

2 + 4 + 8 + 16 = 30 2 + 4 + 8 + 16 = 30

55.

4 1 + 4 1 + 4 2 + 4 6 = 32 3 = 10 2 3 4 1 + 4 1 + 4 2 + 4 6 = 32 3 = 10 2 3

57.

2 + 6 + 12 + 20 + 30 = 70 2 + 6 + 12 + 20 + 30 = 70

59.

1 2 + 2 3 + 3 4 + 4 5 + 5 6 = 71 20 1 2 + 2 3 + 3 4 + 4 5 + 5 6 = 71 20

61.

∑ n = 1 5 1 3 n ∑ n = 1 5 1 3 n

63.

∑ n = 1 5 1 n 3 ∑ n = 1 5 1 n 3

65.

∑ n = 1 5 2 n ∑ n = 1 5 2 n

67.

∑ n = 1 5 ( −1 ) n + 1 3 n ∑ n = 1 5 ( −1 ) n + 1 3 n

69.

∑ n = 1 10 ( −1 ) n 2 n ∑ n = 1 10 ( −1 ) n 2 n

71.

∑ n = 1 7 ( 2 n + 12 ) ∑ n = 1 7 ( 2 n + 12 )

73.

Answers will vary.

75.

Answers will vary.

Section 12.2 Exercises

77.

The sequence is arithmetic with common difference d=8.d=8.

79.

The sequence is not arithmetic.

81.

The sequence is arithmetic with common difference d=−3.d=−3.

83.

11 , 18 , 25 , 32 , 39 11 , 18 , 25 , 32 , 39

85.

−7 , −3 , 1 , 5 , 9 −7 , −3 , 1 , 5 , 9

87.

14 , 5 , −4 , −13 , −22 14 , 5 , −4 , −13 , −22

89.

163 163

91.

131 131

93.

−79 −79

95.

a20=−34.a20=−34. The general term is an=−2n+6.an=−2n+6.

97.

a11=59.a11=59. The general term is an=5n+4.an=5n+4.

99.

a8=−13.a8=−13. The general term is an=−5n+27.an=−5n+27.

101.

a1=11,a1=11,d=3.d=3. The general term is an=3n+8.an=3n+8.

103.

a1=21,a1=21,d=−8.d=−8. The general term is an=−8n+29.an=−8n+29.

105.

a1=−15,a1=−15,d=3.d=3. The general term is an=3n−18.an=3n−18.

107.

1,635

109.

−1 , 065 −1 , 065

111.

360

113.

6,325

115.

–3,575

117.

6,280

119.

4,125

121.

−3,850 −3,850

123.

Answers will vary.

125.

Answers will vary.

Section 12.3 Exercises

127.

The sequence is geometric with common ratio r=4.r=4.

129.

The sequence is geometric with common ratio r=12.r=12.

131.

The sequence is geometric with a common ratio r=−2.r=−2.

133.

The sequence is geometric with common ratio r=12.r=12.

135.

The sequence is arithmetic with common difference d=5.d=5.

137.

The sequence is geometric with common ratio r=12.r=12.

139.

4 , 12 , 36 , 108 , 324 4 , 12 , 36 , 108 , 324

141.

−4 , 8 , −16 , 32 , −64 −4 , 8 , −16 , 32 , −64

143.

27 , 9 , 3 , 1 , 1 3 27 , 9 , 3 , 1 , 1 3

145.

472,392 472,392

147.

3,072

149.

0.0001 0.0001

151.

a9=2,304.a9=2,304. The general term is an=9(2)n−1.an=9(2)n−1.

153.

a15=−219,683.a15=−219,683. The general term is an=−486(−13)n−1.an=−486(−13)n−1.

155.

a10=0.000000001.a10=0.000000001. The general term is an=(0.1)n−1.an=(0.1)n−1.

157.

57,395,624 57,395,624

159.

−65,538 −65,538

161.

7,174,453 59,049 ≈ 121.5 7,174,453 59,049 ≈ 121.5

163.

65,534 65,534

165.

4088 4088

167.

29,524 6561 ≈ 4.5 29,524 6561 ≈ 4.5

169.

3 2 3 2

171.

9 2 9 2

173.

no sum as r≥1r≥1

175.

2,048

177.

1 3 1 3

179.

7 9 7 9

181.

5 11 5 11

183.

ⓐ $6666.67$6666.67 ⓑ $4000$4000 ⓒ $15,000$15,000 ⓒ $7500$7500

185.

$ 295,581.88 $ 295,581.88

187.

$ 14,234.10 $ 14,234.10

189.

Answers will vary.

191.

Answers will vary.

Section 12.4 Exercises

193.

a 8 + 8 a 7 b + 28 a 6 b 2 + 56 a 5 b 3 a 8 + 8 a 7 b + 28 a 6 b 2 + 56 a 5 b 3
+ 70 a 4 b 4 + 56 a 3 b 5 + 28 a 2 b 6 + 70 a 4 b 4 + 56 a 3 b 5 + 28 a 2 b 6
+ 8 a b 7 + b 8 + 8 a b 7 + b 8

195.

p 9 + 9 p 8 q + 36 p 7 q 2 + 84 p 6 q 3 p 9 + 9 p 8 q + 36 p 7 q 2 + 84 p 6 q 3
+ 126 p 5 q 4 + 126 p 4 q 5 + 84 p 3 q 6 + 126 p 5 q 4 + 126 p 4 q 5 + 84 p 3 q 6
+ 36 p 2 q 7 + 9 p q 8 + q 9 + 36 p 2 q 7 + 9 p q 8 + q 9

197.

a 6 − 6 a 5 b + 15 a 4 b 2 − 20 a 3 b 3 a 6 − 6 a 5 b + 15 a 4 b 2 − 20 a 3 b 3
+ 15 a 2 b 4 − 6 a b 5 + b 6 + 15 a 2 b 4 − 6 a b 5 + b 6

199.

x 3 + 15 x 2 + 75 x + 125 x 3 + 15 x 2 + 75 x + 125

201.

y 7 + 7 y 6 + 21 y 5 + 35 y 4 + 35 y 3 y 7 + 7 y 6 + 21 y 5 + 35 y 4 + 35 y 3
+ 21 y 2 + 7 y + 1 + 21 y 2 + 7 y + 1

203.

z 6 − 12 z 5 + 60 z 4 − 160 z 3 + 240 z 2 z 6 − 12 z 5 + 60 z 4 − 160 z 3 + 240 z 2
− 192 z + 64 − 192 z + 64

205.

243 x 5 − 405 x 4 + 270 x 3 − 90 x 2 243 x 5 − 405 x 4 + 270 x 3 − 90 x 2
+ 15 x − 1 + 15 x − 1

207.

27 x 3 − 135 x 2 + 225 x − 125 27 x 3 − 135 x 2 + 225 x − 125

209.

27 x 3 + 135 x 2 y + 225 x y 2 + 125 y 3 27 x 3 + 135 x 2 y + 225 x y 2 + 125 y 3

211.

ⓐ 7 ⓑ 1 ⓒ 1 ⓓ 45

213.

ⓐ 4 ⓑ 1 ⓒ 1 ⓓ 55

215.

m 5 + 5 m 4 n + 10 m 3 n 2 + 10 m 2 n 3 m 5 + 5 m 4 n + 10 m 3 n 2 + 10 m 2 n 3
+ 5 m n 4 + n 5 + 5 m n 4 + n 5

217.

s 7 + 7 s 6 t + 21 s 5 t 2 + 35 s 4 t 3 s 7 + 7 s 6 t + 21 s 5 t 2 + 35 s 4 t 3
+ 35 s 3 t 4 + 21 s 2 t 5 + 7 s t 6 + t 7 + 35 s 3 t 4 + 21 s 2 t 5 + 7 s t 6 + t 7

219.

y 4 − 12 y 3 + 54 y 2 − 108 y + 81 y 4 − 12 y 3 + 54 y 2 − 108 y + 81

221.

q 3 − 12 q 2 + 48 q − 64 q 3 − 12 q 2 + 48 q − 64

223.

625 x 4 − 1000 x 3 y + 600 x 2 y 2 625 x 4 − 1000 x 3 y + 600 x 2 y 2
− 160 x y 3 + 16 y 4 − 160 x y 3 + 16 y 4

225.

243 x 5 + 1620 x 4 y + 4320 x 3 y 2 243 x 5 + 1620 x 4 y + 4320 x 3 y 2
+ 5760 x 2 y 3 + 3840 x y 4 + 1024 y 5 + 5760 x 2 y 3 + 3840 x y 4 + 1024 y 5

227.

126 a 5 b 4 126 a 5 b 4

229.

462 x 5 y 6 462 x 5 y 6

231.

112

233.

324

235.

30,618

237.

Answers will vary.

239.

Answers will vary.

Review Exercises

241.

7 , 13 , 31 , 85 , 247 7 , 13 , 31 , 85 , 247

243.

3 4 , 5 16 , 7 64 , 9 256 , 11 1024 3 4 , 5 16 , 7 64 , 9 256 , 11 1024

245.

a n = 9 n a n = 9 n

247.

a n = e n − 4 a n = e n − 4

249.

a n = − n n + 2 a n = − n n + 2

251.

1 6 , 1 12 , 1 20 , 1 30 , 1 42 1 6 , 1 12 , 1 20 , 1 30 , 1 42

253.

−3 + ( −1 ) + 1 + 3 + 5 −3 + ( −1 ) + 1 + 3 + 5
+ 7 + 9 = 21 + 7 + 9 = 21

255.

4 + 4 + 2 + 2 3 + 1 6 = 65 6 4 + 4 + 2 + 2 3 + 1 6 = 65 6

257.

∑ n = 1 5 ( −1 ) n 1 3 n ∑ n = 1 5 ( −1 ) n 1 3 n

259.

∑ n = 1 5 4 n ∑ n = 1 5 4 n

261.

The sequence is arithmetic with common difference d=6.d=6.

263.

5 , 8 , 11 , 14 , 17 5 , 8 , 11 , 14 , 17

265.

−13 , −7 , −1 , 5 , 11 −13 , −7 , −1 , 5 , 11

267.

−129 −129

269.

a18=103.a18=103. The general term is an=7n−23.an=7n−23.

271.

a1=1,a1=1,d=4.d=4. The general term is an=4n−3.an=4n−3.

273.

−1,095 −1,095

275.

585 585

277.

4,850 4,850

279.

980 980

281.

The sequence is not geometric.

283.

The sequence is geometric with common ratio r=−2.r=−2.

285.

128 , 32 , 8 , 2 , 1 2 128 , 32 , 8 , 2 , 1 2

287.

1,536 1,536

289.

a12=−25,165,824.a12=−25,165,824. The general term is an=6(−4)n−1.an=6(−4)n−1.

291.

−43,692

293.

3906.25 3906.25

295.

189 8 = 23.625 189 8 = 23.625

297.

343 6 ≈ 57.167 343 6 ≈ 57.167

299.

4 11 4 11

301.

$ 1,634,421.27 $ 1,634,421.27

303.

x 4 − 4 x 3 y + 6 x 2 y 2 − 4 x y 3 + y 4 x 4 − 4 x 3 y + 6 x 2 y 2 − 4 x y 3 + y 4

305.

32 y 5 − 240 y 4 + 720 y 3 − 1080 y 2 32 y 5 − 240 y 4 + 720 y 3 − 1080 y 2
+ 810 y − 243 + 810 y − 243

307.

ⓐ 11 ⓑ 1 ⓒ 1 ⓓ 56

309.

ⓐ 1 ⓑ 1 ⓒ 1 ⓓ 55

311.

t 9 − 9 t 8 + 36 t 7 − 84 t 6 + 126 t 5 t 9 − 9 t 8 + 36 t 7 − 84 t 6 + 126 t 5
− 126 t 4 + 84 t 3 − 36 t 2 + 9 t − 1 − 126 t 4 + 84 t 3 − 36 t 2 + 9 t − 1

313.

256 x 4 + 768 x 3 y + 864 x 2 y 2 256 x 4 + 768 x 3 y + 864 x 2 y 2
+ 432 x y 3 + 81 y 4 + 432 x y 3 + 81 y 4

315.

84 a 3 b 6 84 a 3 b 6

317.

135

319.

280

Practice Test

321.

1 4 , 1 5 , 1 6 , 1 7 , 1 8 1 4 , 1 5 , 1 6 , 1 7 , 1 8

323.

−4 + 16 − 64 + 256 = 204 −4 + 16 − 64 + 256 = 204

325.

−13 , −10 , −7 , −4 , −1 −13 , −10 , −7 , −4 , −1

327.

a23=59.a23=59. The general term is an=3n−10.an=3n−10.

329.

1,325 1,325

331.

3,260 3,260

333.

The sequence is geometric with common ratio r=13.r=13.

335.

5,242,880 5,242,880

337.

797,162 797,162

339.

5 6 5 6

341.

$ 1,409,344.19 $ 1,409,344.19

343.

ⓐ 8 ⓑ 1 ⓒ 1 ⓓ 210